1. Field of the Invention
The present invention relates to a separator and, more particularly, to a sloped screen separator that removes solids from a manure slurry.
2. Description of the Related Art
When waste, such as manure, is washed away with a stream of flush water, a waste or manure slurry is formed. In agriculture, enclosed animal areas are commonly flushed with water. For example, in the dairy industry, the alleys in a freestall barn are typically flushed twice a day with water to clean the manure from the alleys.
The treatment of manure slurry is a difficult and on-going problem in many agricultural settings. One approach to treating manure slurry is to fill large settling pits or lagoons with the slurry. Gravity then pulls the larger solids to the bottom. The surface water, which contains fewer solids, is typically pumped to another lagoon, where the process is repeated. The surface water of the last lagoon is then pumped out to irrigate agricultural lands, such as alfalfa fields, or used again to flush accumulated manure from animal areas.
This approach, while relatively straightforward, has a number of drawbacks. One drawback is that the accumulated solids in the lagoons have to be periodically removed at a significant expense. Another drawback is that the longer the manure stays in suspension within the slurry, the more nutrients transfer from the solids to the water.
This loads the water with very high levels of nitrogen, phosphorous, and salts. A high loading, in turn, limits the amount of irrigation that can be performed, or requires the addition of fresh water to change the loading of the water. A further problem is that a significant amount of gas, such as ammonia and sulfer, escapes from the slurry in a lagoon, thereby contributing to air pollution.
A common modification to this approach is to run the manure slurry through a separator to remove as many solids from the slurry as possible. By removing solids from the slurry, fewer solids are deposited in the lagoons. Reducing the amount of solids that are deposited into a lagoon increases the useful life of the lagoon, reduces the loading of the water (because solids are removed from the water), and reduces air pollution. One type of separator is a sloped screen separator.
FIG. 1 shows a cut-away perspective view that illustrates a conventional sloped-screen separator 100, while FIG. 2 shows a side view of separator 100. As shown in FIGS. 1-2, separator 100 has a back wall 110, and first and second side walls 112 and 114 that are connected to back wall 110. Side walls 112 and 114, in turn, have openings 116 and 118.
In addition, separator 100 has a top panel 120 that is connected to the top ends of side walls 112 and 114, and a lower panel 122 that is connected to the bottom ends of back wall 110 and side walls 112 and 114. Lower panel 122, in turn, has an opening 124.
Separator 100 also has a ledge 130 that is connected to side walls 112 and 114, and a trough 132 that is connected to back wall 110, side walls 112, and ledge 130. Trough 132 has a bottom side 134, and an opening 136 formed in bottom side 134. Separator 100 further includes a baffle 140 that is connected to side walls 112 and 114 over the longitudinal center of trough 132.
As further shown in FIGS. 1-2, separator 100 has a front edge 142 that is connected to side walls 112 and 114 and lower panel 122, and a sloped screen 144 that is connected to side walls 112 and 114, ledge 130, and front edge 142. Sloped screen 144 typically has slotted or circular openings of 1.5 mm (approximately 0.060 of an inch).
In operation, manure slurry is pumped into trough 132 through opening 136. Baffle 140 spreads the incoming slurry so that the slurry flows evenly over the edge of ledge 130 onto sloped screen 144. The slurry flows through screen 144, with screen 144 extracting the larger solids from the slurry.
Gravity pulls the larger solids extracted by screen 144 down the face of screen 144. The solids accumulate at the bottom of screen 144, and eventually fall off of front edge 142 where the solids are collected as stackable manure. In the dairy industry, stackable manure has a moisture content of roughly 75-80%.
One problem with separator 100 is that separator 100 is relatively inefficient. Experimental results indicate that separator 100 removes, at best, approximately 16% of the solids in the slurry. Thus, even though separator 100 removes solids from the slurry, large amounts of solids continue to be added to the lagoons.
Screens with smaller openings are not utilized because the solids in the slurry plug the openings. When the openings in the screen become plugged, all the slurry pumped into opening 136 of trough 132 runs down the face of screen 144 and falls off of front edge 142, causing slurry to be pumped into the work yard. The resulting clean up can be a significant expense. Thus, due to plugging, screens with openings equal to or less than 1.0 mm (approximately 0.040 of an inch) are considered to be unworkable.
With separator 100, the slurry falls through screen 144 and is collected by lower panel 122. The slurry then flows out opening 124 where the slurry is gravity fed to a lagoon. The flow of slurry into opening 124 creates a suction. If openings 116 and 118 were absent or closed, the suction would pull air through screen 144. The flow of air through screen 144, however, pulls and holds solids to screen 144, thereby plugging the openings. Thus, openings 116 and 118 provide an air intake route that eliminates the suction across screen 144 so that larger solids can fall down the face of screen 144.
Screen 144 is also subject to plugging from hot summertime conditions. When the available slurry has been pumped through separator 100, solids to varying degrees remain on the face of screen 144. In hot summertime conditions, the solids quickly dry. When the slurry is again pumped into separator 100, the initial slurry runs down the face of screen 144 and falls off front edge 142 until the moisture in the slurry unplugs the openings.
One approach to preventing summertime conditions from plugging screen 144 is to mist the face of screen 144 when slurry is no longer being pumped into separator 100. This can be accomplished by placing a water line with a number of mist heads across the front of screen 144.
When the water line is connected to a water source under pressure, such as 2.46 kilograms per square centimeter (approximately 35 pounds per square inch) to 3.87 kilograms per square centimeter (approximately 55 pounds per square inch), the mist heads output mist in the range of 2.65 liters per hour (approximately 0.7 gallons per hour) to 4.9 liters per hour (approximately 1.3 gallons per hour). The level of misting should not cause solids to move down or sheet down the face of screen 144.
Thus, although sloped screen separators reduce the volume of solids that are deposited into the holding lagoons, there is a need for a separator that removes more solids from the manure slurry.